The present invention relates to a network system, method and computer program constructed in a Local Area Network (LAN). More particularly, the present invention relates to an automatic address distributing method, computer program and system having a function for distributing addresses each serving as identification information of each terminal connected to the LAN.
With the development of network systems, there have been encountered problems that the amount of work load in system construction and management increases and addresses each serving information for uniquely identifying each terminal connected to a network become obsolete. In order to solve the problems, there have been proposed methods of automatically distributing an address which can be used only for a fixed period of time to each terminal connected to a network.
A representative one of the methods is a Dynamic Host Configuration Protocol (DHCP) described in the DHCP Network Working Group Requests for Comments (RFC) by R. Doms, IETF, October 1993, information on standardizations open to the public. The DHCP allows the amount of work load in the system construction and management to be reduced and makes efficient use of addresses possible.
A point in the dynamic distribution of addresses according to the conventional technology to which attention should be paid is that the same address as one used for a terminal connected to the network must not be distributed to another terminal, that is, duplicate assignment of an address must be avoided. There are two techniques for addressing this problem.
According to a first technique addresses used in a network are examined in advance. The addresses found used in an existing network by the examination conducted in advance are never cataloged in a database used for storing addresses to be distributed by the server having a function for distributing addresses by the DHCP so as to avoid duplicate assignment of an address.
According to a second technique, in order to avoid duplicate assignment of an address by the DHCP, a packet is transmitted to an address to be assigned to a terminal prior to the distribution of the address. In this way, it is possible to determine if the address has been assigned to an existing terminal connected to the network.
The first technique has a problem that an additional work load for examining and cataloging addresses is introduced. Depending upon the size and complexity of the network, the problem caused by the additional work load may be severe.
The second technique has a problem that it may not be possible to examine whether or not a terminal having the same address as the one to be distributed exists due to the following reasons:
1) The terminal is in an off-line state due to, for example, the fact that the power supply thereof is turned off,
2) Because of network congestion, the transmitted packet is lost, and
3) The terminal is moved from the current network to another network with network information relevant to the terminal such as the address thereof left in the current network.
The shorter the period of time in which a distributed address can be used, in other words, the shorter the validity period of a distributed address, the higher the utilization efficiency of the address. However, a packet is required for requesting that the period of time or the validity period be extended. Transmission of such packets gives rise to a problem that the traffic of the network becomes excessively heavy.
It is an object of the present invention to provide an automatic address distributing method, computer program and system for automatically examining addresses already assigned to terminals connected to a network without regard to the status of the existing terminals and removed terminals.
It is another object of the present invention to provide an automatic address distributing method, computer program and system that eliminates packets for requesting extension of the validity periods of distributed addresses with the efficient use of distributed addresses kept as it is.
In order to achieve the objects described above, the present invention provides an automatic address distributing system having an address distributing server in a network system for automatically distributing network information including address information to terminals connected to the network system. The address distributing server includes a duplicate-address examining apparatus for automatically examining addresses already used by the terminals prior to distribution of an address and an in-use-address storing apparatus for storing examination results produced by the duplicate-address examining apparatus, thereby avoiding distribution of a duplicate address of an address already used in the network system.
The network system further includes a name server for controlling relations between terminal addresses and host names. The duplicate-address examining apparatus examines addresses used by the terminals connected to the network system by making an inquiry to the name server.
The network system further includes a mobility agent for monitoring as well as supporting a movement of a terminal from the network system to another network system. The duplicate-address examining apparatus examines an address used by a terminal having moved to another network system by making an inquiry to the mobility agent.
In addition, the present invention also provides an automatic address distributing system having an address distributing server in a network system for automatically distributing network information including address information to terminals connected to the network system. The network system includes a mobility agent for supporting a movement of a terminal from the network system to another network system and the address distributing server includes a storage apparatus for storing information on the mobility agent. The address distributing server receives a message transmitted by the mobility agent, wherein the message is used to obtain information on a location and movement of a terminal connected to the network system, and automatically stores information conveyed by the message from the mobility agent in the storage apparatus.
Furthermore, the present invention also provides an automatic address distributing system having an address distributing server in a network system for automatically distributing network information including address information to terminals connected to the network system. The address distributing server includes a storage apparatus for storing an initial validity period, a current validity period and the number of validity-period extensions of each distributed address, thereby dynamically modifying the validity period of a distributed address in response to a request for an extension of the validity period made by a terminal owning the distributed address.
In addition, the address distributing server notifies a terminal owning a distributed address of an extended validity period derived by extension of the current validity period by a product of the initial validity period and the number of validity-period extensions in response to a request for an extension of the validity period made by the terminal.
Furthermore, when an address is distributed to a terminal which used the same address previously, the address distributing server notifies the terminal of a current validity period of the distributed address which is derived by using the previous validity period of the distributed address.
The present invention further provides a method and computer program each having steps corresponding to the functions described above with respect to the embodiments of the automatic address distributing system.